Abstract

On the basis of their vegetation and soils, sub-Antarctic island ecosystems are considered to be part of the tundra biome. However, sub-Antarctic
island vegetation is more productive and nutrient cycling more rapid than in Northern Hemisphere tundra. Human occupation
and exploitation on the islands has comprised mainly sealing, whaling and, in some instances, fishing and agriculture, Research stations
have also been established for meteorological monitoring and scientific research. All these activities have affected the islands' floras and
faunas but the greatest impact of humans has been through the introduction of alien organisms. Because the islands' indigenous biotas
are species-poor and lack cardinal trophic groups that are common in other ecosystems (especially mammalian herbivores and predators),
an introduced species that becomes invasive on an island can have insidious, but far-reaching, efFects on ecosystem functioning. Such
effects are the focus of this paper and the principal examples given are the effects of the introduced house mouse and a European slug on
nutrient cycling at Marion Island. Manuring by seabirds and seals is also an important determinant of ecosystem structure and function
at sub-Antarctic islands. Introduced domestic cats have reduced burrowing bird populations on some of the islands, and at Marion Island
the populations of most surface-nesting birds have also declined, probably due to human exploitation of their oceanic food resources.
This has far-reaching implications for ecosystem functioning. The sub-Antarctic region is also becoming warmer; at some islands this is
coupled with decreased, and at others with increased, precipitation. Some implications of these climatic changes for ecological functioning
are presented. 'The most important is that a warming climate will increase the probability of introduced organisms becoming established
on an island. 'ibis, together with increasing human visitation and occupancy (the major cause of species introductions), implies that it is
inevitable that the rate of establishment of invasive biota on the sub-Antarctic islands will increase.